This invention relates to keypads with push buttons and in particular to integrating different parts of a keypad to provide better and more secure functioning.
The known keypads in portable electronic devices comprise a cover portion and different key portions. These two separate parts are located so that the key portion comes through the cover portion. The keytops, which are situated outward from the cover, move into an inward direction with respect to the cover when pressed. This provides tactile feedback to user. Another important thing for the user is that each key is identified by printing some markings or characters on the outer surface of a key or by embossing the flexible cover to create raised areas at or around the keytop locations.
FIG. 1a is a sectional exploded view, which illustrates a known structure of a keypad. These kinds of keypads are used for example in mobile telephones and personal digital assistants. The upper surface of a printed circuit board 101 comprises a number of contact areas, where at least two conductive strips 102 and 103 come close to each other. Supported over the printed circuit board 101 and separated from it by a perforated insulation layer 104 is an array of conductive domes 105 so that each conductive dome 105 lies directly above the conductive strips 102 and 103. Key mat 106 is located on top of the conductive domes. It is made of an elastic material. A bulging protrusion 107 of the key mat protrudes slightly out through the holes in the outer cover 108. In some keypads hard key-specific parts are used above the bulging protrusions 107 to provide a harder tactile feeling for the user (not shown in FIG. 1). FIG. 1b shows the same structure in assembled configuration.
A cover portion 108 is the outer part of the structure in FIGS. 1a and 1b. In these figures the key mat 106 and the bulging protrusions 107 form a key portion. The rest of the structure, a printed circuit board 101, conductive strips 102, 103, a perforated insulation layer 104 and conductive domes 105 form the actual electrically functioning part of the keyboard.
One problem with prior art keypad is printing desired markings or characters on the surface of each key. Such printing operation should be performed directly on the surface of the each individual key or button. These buttons have substantially cubic configuration. This kind of printing operation is complex and less efficient compared to the printing operation in which a marking or the like is directly printed on a sheet. It is also difficult to perform a fine printing. Also it is noted that, when a plurality of keys are simultaneously printed with a marking, misregistration between the keytops and a printing means would occur, since the keytop plate has flexibility. As a result, simultaneous printing of a marking or the like on number of keytops is impossible. This reduces the efficiency of the printing operation.
Another unsolved problem of the prior art solutions raises from the fact that there must be an interstice between the key portion and the cover portion for the keytop to be able to move. The final product should be as compact as possible, so the interstice between the key portion and the cover portion should be kept small. Advantageously this interstice should be smaller than 0.5 mm. On the other hand in the mould there must be accomplished a closing surface to the interstice. This provides that the cover should be thicker than 0.5 mm.
In the publication U.S. Pat. No. 6,064,019 there has been introduced a resilient switch cover and an actuator button compactly installed through the aperture in the cover. Compactness of the solution of this patent is based on the size of the button, which is larger in diameter than a corresponding diameter of the aperture in the cover.
In the publication U.S. Pat. No. 6,023,033 there has been described a method for producing a keytop plate. In this solution the keytops are formed by moulding a resin at the predetermined positions of a synthetic resin film. A moulded elastomer plate is attached to formed keytops. The waterproofing capability of this construction is based on the fact that in the area of the moulded elastomer plate, other than the areas to which the keytops are attached, there are no through-holes.
It is also known by the prior art to isolate a separate key by some soft substance. All prior art solutions are generated with number of separate manufacturing steps, which often require number of different moulds and intermediate storages. These different production steps are usually expensive and inefficient.
The object of the present invention is to overcome the drawbacks of the prior art. A further object of the present invention is to simplify the manufacturing and to produce a compact keypad resistant against harmful environmental effects.
The objects of the invention are achieved by integrating the key portion to the cover portion. This new configuration packs the keys and the cover to one solid and essentially rigid portion, which is manufactured in a limited number of steps. Further a soft component is attached to the rigid component to make the construction resistant against harmful environmental effects.
The invention is directed towards the features of the keypad, which are described in the independent claims. According to the present invention the keypad is characterized in that it comprises a first component including a cover portion and a key portion that form together a single structural entity so that said structural entity allows the key portion to move within a limited range in relation to the cover portion; and a substantially soft second component, which is attached to the first component for covering space between the cover portion and the key portion of the first component and making composed compound construction substantially tight, still allowing the limited movement of the key portion of the first component.
According to the present invention there is produced a rigid component, which includes a cover portion and a key portion, and a soft component, which makes the configuration tight. The different structures in the rigid component are generated by components having certain mechanical characters. For example in fixed, hard parts there is simply a thicker material layer while in flexible parts a thin layer is used. Also in the mechanical construction different shapes are used knowing the fact that planar structures can be used in flexible parts of the component, whereas for the hard, rigid parts for example a cubic-like or dome structure would be more appropriate. The soft component is attached to the rigid component either mechanically or chemically.
The new compact construction introduced in the present invention is easier and cheaper to manufacture, because the rigid component can be moulded in one mould. The whole structure can be generated with a conventional mould without any moving parts. This has the further advantage that also the manufacturing process is stable, so it includes less variables and can be carried out effectively.
In the keypad structure of the present invention, there is a certain interstice between the keytop and the cover, although these parts are made as one rigid component.
The soft component covers the interstice and makes the structure compact. The soft component so prevents dirt and dust from penetrating inside the structure, as dirt and dust might otherwise cause a key to stick or not to function properly. All these kind of problems are solved by the present invention. Also with the proper choice of the materials and substrates water resistance may be achieved.
The tactile characteristics of this new construction make the use of the product comfortable. If the whole keypad would be made of flexible material, the tactile feeling and feedback would remain relatively soft. A hard tactile feeling, which is preferable to most users, may be provided by a moulded construction introduced here. With a harder tactile feeling the user can be more secure about her/his selections. The more the depth-directional movement is needed, the more there must be space surrounding the moving parts either in vertical or horizontal direction.
The graphics or, in the other words, printing markings and characters on the pushbuttons, may be carried out easily with this new construction presented in this invention. Now graphics can be implemented even in the mould, and/or printing operations can either be done straight on the key made of rigid component or to the soft component area.